Sound recording



May 23, 1933.

A. c. KE; L5R

SOUND RECORDING Filed ooi. so, 1929 Patented May 23, 1933 PATENT OFFICE UNITED STATES ARTHUR C. KELLER, OF NEW YORK, N. Y.,

ASSIGNOR TO BEL-L TELEPHONE LABORA- TORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK SOUND RECORDING Application ilcd October 30, 1929. Serial No. 403,492.

This invention relates to sound recording and reproducing systems and particularly to those capable of embracing a range of fre quencies in excess of the present high quality range.

It is the object of the invention to provide means for utilizing a single groove as a record of variations in two or more frequency bands Prior to this invention it has been proposed as in Aifel Patent 1,595,135, granted Aug. 10, 1926 to split a band of speech frequencies into a number of sub-bands for separate transmission over circuits each of which, due to linherent limitations, is incapable of transmitting the Whole band. Suitable means is then provided at the receiving point to reassemble the components into the original band. Also in Lindridge Patent 1,675,894, granted July 8, 1928 it was proposed to apply this general idea to a recording system in which the record material had inherent limitations analogous to those of Aels transmission circuits.

In my copending application Serial No. 402,128, filed Oct. 24, 1929, there is disclosed a sound reproducer capable of responding to a range of frequencies much in excess of the present commercial high quality band which may be said to extend up to about 4500 cycles.

The necessary design formula and general instruetions are given in that application for 'designing a rep-roducer capable of responding to the complete audible range and also to higher frequencies. It is also novi7 possible to design recorders capable of making a satisfactory record of frequencies much in excess of the commercial range mentioned above.

ln accordance with the present invention, 40 therefore, it is proposed by the use of such novel recorders and reproducers to make an entirely new form of record, namely, one in which the sounds from tWo or more separate sound sources, each embracing a range of frequencies suiiicient for good quality sound reproduction, are recorded in the same record groove. According to the preferred method of carrying out the invention the frequencies r representing the various extra record bands 'J0 are displaced in the frequency scale by modulation to form a progressive series of bands separated by suitable intervals. This composite band is then recorded on a record blank of the proper physical characteristics for such a Wide range of frequencies, and in the reproducing circuit the bands are separated by filters and restored to their original position in the frequency scale for reconversion into sound through separate receiving means.

lt will be understood, of course, that the invention is not limited to making a uni tary Arecord of several similar frequency bands for it is also contemplated that it may be desirable to pick up and record vibrations above the ordinary audible range either separately or together with the usual sound frequencies. For instance the invention may be employed for simultaneously recording for subsequent study and analysis the currents representing speech and those representing transient disturbances in telephone circuits.

The following detailed description of one embodiment of this invention is given by Way of illustration but obviously many modif`1- cations Within the scope of the invention will occur to those skilled in the art desiring to use such a recording and reproducing system for special purposes.

1 of the drawing illustrates schematically the essential apparatus and connections for recording and reproducing a record according to the invention and Fig. 2 is a similar schematic of a recording system in which vibrations of different frequency ranges are directly recorded.

In Fig.A 1, 1, 2 and 3 are shown as conventional microphones but it should be undei-stood that one or more of them may represent t'otally different sources of alternating currents as for instance a telephone line oi other electric circuit. An amplifier 4 is provided at each source and the vibrations from microphone 1, Which would ordinarily be Within the .sound range of GO-iSOO cycles, arc further intensified by amplifier 5 and registered by recorder 6 .on the record 7 which is rotated by turntable 12. The vibration source 2V may deliver a similar band of frequencies representing music or pressure variations through its amplifier 4 to modulator 8 which by means of suitable carrier frequency supplied by oscillator 9 displaces the band to the 5060 to 9500 cycle range in the well known manner.

Similarly, modulator 10 and oscillator 11 will shift the 60 to 4500 cycle currents from source 3 to the 10060 to 14500 cycle range and both these ban-ds of higher frequencies will also be recorded by recorder 7, superimposed upon the ordinary record.

In the reproducing system the original record 7 or a pressing 13 made from it is rotated by turntable 14. Re roducer 15 is of a type such as that descri )ed in my copending application already mentioned, which is capable of responding to the highest frequency recorded and the currents generated by it are raised to a suitable level by amplifier 16. Band pass lter 17 is of the low pass type so that only the frequencies recorded without modulation, in this case (S0-4500 cycles will be passed to amplifier 18 associated with recefver 19. Filter 20 is ada ted to pass only the frequencies recorded 1n the 5060-9500 cycle range and this band by means of oscillator 21 and demodulator 22 is displaced to its original position in the -4500 cycle range for conversion into sound through its receiver 23. Similarly, filter 24 selects the 10060-14500 cycle band and this is also shifted back to its original position and transmitted to receiver 25.

In Fig. 2 the devices 26 and 27 may be microphones or any other Sources of electrical variations of different fre uency ranges, such as speech and superaudi le variations, respectively, and as they are already se arated by a sufficient frequency interval tlIijey may be amplified and transmitted directly to the recorder 31 without modulation. In reproducing the record 32, however, it would be necessary to use suitable discriminating apparatus such as that shown in Fig. 1, for se arating the two bands.

at is claimed is:

1. In a recording system, a record blank and means for recording thereon in the same groove a high quality sound record and a separable record of a band of frequencies extending above the range of the high quality sound record.

2. In a recording and reproducing system, a plurality of sources of frequency bands each embracing the high quality sound range, means for transposing certain of the bands to produce a progressive series of bands separated by suitable frequency intervals and including the usual speech range, a record blank and means for recording the series of bands on the record blank, unitary means for reproducing the series of bands, means for retransposing the bands to their original position in the frequency scale and receiving means for each of the reproduced bands.

3. In a recording and reproducing s stem a plurality of sources of frequency ands each embracing the high quality sound range, means for increasing the amount of matter which may be recorded on a single record blank comprising modulators for transposing certain of the bands to form a progressive series of bands separated by suitable frequency intervals, a record blank and means for recording the series of bands on the rocord blank, unitary means for reproducing the series of bands, band pass filters for separating the reproduced frequencies into the original number of bands, demodulators for restoring the separated bands to their original frequency ranges, and receiving means for the restored bands.

4. In a recording and reproducing system a plurality of microphones each picking up frequency bands embracing the hifrh qualit sound range, vacuum tube amplifiers for eac band, means for increasing the amount of matter which may be recorded on a sin le record blank comprising modulators or transposing said bands into a progressive series of bands separated by suitable frequency intervals, a vacuum tube am lilier for the series of bands, a record blan and a recorder capable of recording the entire series of bands on the record blank, a re producer for reproducing the recorded frequencies, a vacuum tube am lifier for strengthening the reproduced requencies, band pass filters for separating the reproduced frequencies into the original number of bands, demodulators for restoring the bands to their original frequency ranges, and receiving means for reproducing all of the restored bands.

5. In a recording system a. record blank and means for recording thereon in the same groove frequencies representing sounds from at least two separate sources, certain of said sounds being represented in the record by corresponding frequencies and other sounds being represented by frequencies higher than the original sounds.

In Witness whereof, I hereunto subscribe my name this 28th day of October, 1929.

ARTHUR C. KELLER. 

